Volatile organic compounds (VOCs) are chemical species emitted by certain solids or liquids commonly used in industrial and household products, but many of them pose severe risks to human health and may form explosive mixtures in air. In particular, VOCs with aromatic moieties, such as benzene, styrene, toluene, and xylene, are considered carcinogenic, can cause adverse health effects upon short-term exposure, and form explosive mixtures in air at concentrations as low as 1 vol. % in air.1-3 However, the lack of chemically reactive functionalities in these molecules means that they are difficult to detect using conventional electrochemical detection methods.
Commercial methods of detection of this type of VOCs often involve off-site analytical methods or centralized detection equipment, such as colorimetric detectors, photoionization detectors, or portable infrared spectroscopes. These methods of detection can be expensive, and they do not provide information about personal exposure monitoring. In many occupational settings, the local concentrations of VOCs to which a person is exposed might reach levels much higher than those being measured several feet away by centralized detection equipment.4,5 
Accordingly, there is a need in the art for technologies that could be used to develop cheap, wearable devices for monitoring personal exposure to aromatic VOCs. In particular, there is a need for power-free devices that are able to detect local concentrations of VOCs and to retain a history of exposure to VOCs. Such devices could be used in, for example, occupational hygiene, chemical storage sites, and equipment for first-responders.
A problem associated with liquid crystal-based technology is that films of liquid crystal (LC) supported on a solid substrates tend to deform and dewet. Previous approaches aimed at stabilizing LC films having a thickness in the micrometer range include the use of metal grids, polyurethane microwells and micropillar arrays. In the case of the grids and the polyurethane wells, manual filling is tedious and not practical for manufacturing, and makes it difficult to precisely control the LC thickness. High density arrays of micropillars use capillary forces to stabilize LC films, but they generate significant distortions of the director that might influence the behavior of the LC and they are difficult to reproducibly fill. Moreover, it can be difficult to control the surface chemistry of the micropillar arrays. The LC also tends to dewet the micropillars at the edge of the array.
Accordingly, there is a need in the art for methods and devices that allow for precise control of thickness and control of the surface anchoring conditions of LC films disposed on surfaces.